1. Field
Exemplary embodiments relate to a method of manufacturing a ferritic/martensitic steel used in a nuclear power reactor, and more particularly, to a method of manufacturing a high strength ferritic/martensitic steel that may possess a high strength even in a high-temperature environment.
2. Description of the Related Art
General ferritic/martensitic steels containing 9 to 12 wt % of chrome may have high thermal conductivities, low expansion coefficients and excellent neutron irradiation resistances, and these steels may be used extensively as nuclear fuel cladding tube materials and structural materials in a fast reactor, a fusion reactor, and the like.
With respect to the manufacturing process of nuclear fuel cladding tubes of the high chrome ferritic/martensitic steel, a raw material may be melted by a vacuum induction melting process, a hot-working, a heat treatment, a cold-working, and a final heat treatment (normalizing and tempering) may be sequentially performed. Here, the hot-working may denote a hot-forging process and a hot-extrusion process, and the cold-working may denote a cold-pilgering process and a cold-drawing process. The normalizing and tempering of the final heat treatment may be respectively performed at a temperature of about 1050° C. to 1150° C. and a temperature of about 730° C. to 780° C., and a time required for the heat treatment may be determined by a thickness of the steel.
The high chrome ferritic/martensitic steel manufactured as described above may have limits to improving strength of the steel obtained by changing a temperature of the heat treatment after the hot-working or manufacturing variables such as in the cold-working, the final heat treatment, and the like. In particular, in a high-temperature environment of about 600° C. or more, a yield strength and a tensile strength may be deteriorated.